Such cellular plastic covers have been used successfully on swimming pools, with air-cells, either cylindrical or hemispherical in form, in a range of diameters of typically 5/16" for the cylindrically shaped cells, to 1" for the hemispherical form, and of heights from about 1/8" to 5/16" for the cylindrical cells, to about 5/16" for the hemispherical form. These dimensions are given herein as examples, but in no way as limitative on the invention. The covers are preferably used with the sheet having the protuberant air-cells on the underside, projecting downward, and in the ensuing description, this orientation will be assumed, but without limitation thereto. Such covers are adapted also for use on ponds, in sizes greater than those typical of swimming pools.
Such covers, having a specific gravity less than that of water, float on the water, the upper surface of the cover riding normally at approximately from 75% to 95% of the vertical thickness of the cover (from top surface of upper sheet to bottom surface of cell) above the water line depending upon the specific gravity of the cover.
Such covers are now in fairly widespread use on swimming pools, and are known to utilize importantly solar energy for heating of the pool water, to limit evaporation, thus conserving heat otherwise lost in the evaporative process, or through heat radiation, and also conserving chemicals lost with the evaporating pool water. The cost of such a cover may be recovered by these savings within only a few months.
It has previously been proposed to subdivide swimming pool covers into separate floating units. Experience has shown, however, that the edges of unit covers often turn upwards, so as to rise above the water in local regions, and thus catch wind, which lifts or whips them higher, or partially over, and fairly large undesirable folds thus develop which disarrange the cover units, pull them back from the pool edges, separate them, overlap them, and generally shift them into non-conformature with the intended generally flat and well-fitting orientation on the pool water. Swimming pool cover units have also been proposed composed of a circular plastic sheet, bounded by an upstanding rim. These have the problem, however, that the rim, which enables them to float, like a boat, permits splash water caught in them to cause them to sink. One general purpose of the invention is to deal effectively with these problems.